Endothelins are peptides that exist in three isoforms, ET-1, ET-2, and ET-3, each encoded by a distinct gene. They have been originally discovered in the conditioned medium of porcine endothelial cells in 1988 by Yanagisawa (Yanagisawa M; Kurihara H; Kimura S; Tomobe Y; Kobayashi M; Mitsui Y; Yazaki Y; Goto K; Masaki T: A novel potent vasoconstrictor peptide produced by vascular endothelial cells [see comments]. NATURE (1988 Mar. 31), 332(6163), 411–5. ). The active ETs are peptides of 21 amino acids with two intramolecular disulfide bridges. They are produced from preproproteins of 203 to 212 amino acids, which are processed by furin-like endopeptidases to the biologically inactive big-endothelin (big-ET). The big-ETs are specifically processed to mature ETs by a hydrolytic cleavage between amino acids 21 and 22 that are Trp21-Val22 (big-ET-1, big ET-2) and Trp21-Ile22 in big-ET-3 respectively. Already in 1988 a specific metalloprotease was postulated to be responsible for this specific cleavage. In 1994 ECE-1 (endothelin converting enzyme-1) was purified and cloned from bovine adrenal (Xu D, Emoto N, Giaid A, Slaughter C, Kaw S, de Witt D, Yanagisawa M: ECE-1: a membrane-bound metalloprotease that catalyzes the proteolytic activation of big endothelin-1. Cell (1994) 78: 473–485).
ECE-1 is a membrane bound type II zinc-endopeptidase with a neutral pH optimum and a zinc binding motif HExxHx(>20)E. It belongs to subfamily M13 and has a large 681 amino acid ectodomain that comprises the active site. Other members of the M13 family are NEP24.11 (neutral endopeptidase), PEX, a phosphate regulating neutral endopeptidase, and Kell blood group protein that has recently been described as a big-ET-3 processing enzyme. Members of the M13 family of human origin are characterized by a high molecular weight (>80 kDa) a number of conserved disulfide bridges and a complex glycosylation pattern. The structure of NEP has recently been solved. (Oeffer et al, J. Mol. Biol. 2000, 296, 341–349). The catalytic domain of ECE and related human M13 proteinases are significantly larger (>650 amino acids) than members of matrix metalloproteases (MMPs). Unlike the family of the MMPs which belong to the metzincins and display a typical HExxHxxGxxH pattern members of the M13 family are gluzincins comprising a HExxHx(>20)E pattern. These two families are clearly different in size of catalytic domains, structure and zinc coordinating pattern of ligands. Active sites of the two families show clear differences which has clear impact on type of inhibitors and the potential selectivity.